are you jim? >> what's up? >> reporter: which brings us back to that familiar scene and that plastic bag. tell me what i'm looking at here, syringes, one bottle. >>> how do i know that it's authentic? >> see the numbers here? >> reporter: sure enough. what appears to be an authentic bottle of the popular steroid gpsust. >> over time they cause tremendous, tremendous harm. strokes, cancer of the liver, pancreatitis. >> reporter: dr. harris says the side effects are even more threatening to a teenager's body. and according to a study published in the journal pediatrics, one in 20 students has used steroids for muscle growth. the largest group not athletes. according to findings by fenway substitute, gay teens are nearly six times more likely to use. >> they said to themselves if i do steroids, i'll build myself up, and i'll become very muscular. i can defend myself and i'll look better. >> reporter: there is no one single source for where these drugs enter the black market. jamie says he gets his from medicine ca